Justice Department lawyers are challenging what they term an “enormous” error by a Houston federal judge with a history of bucking up against prosecutors, saying he erred gravely when he “radically reduced” the sentence of an admitted ISIS supporter who attempted to join the jihadist cause overseas.

Attorneys from the Justice Department’s national security arm filed the appeal Friday with the Fifth U.S. Circuit Court of Appeals to address the unprecedented 18-month prison term that U.S. District Judge Lynn N. Hughes issued to Asher Abid Khan in June 2018. Federal probation officials had advised the judge to sentence Khan to more than 20 years, according to the government prosecutors.

The sentence, according to the appeal, “Did not reflect the gravity of Khan’s conduct and would not sufficiently deter others from taking the first step along the path to radicalization."

“The district court’s error was not harmless,” the government argued in its filing. "Indeed, the magnitude of its error was enormous.”

Khan, 24, of Spring, was continuing his mechanical engineering studies at the University of Houston up until he reported to prison. He pleaded guilty to recruiting a high school friend to join ISIS militants in Syria. He had intended to join as well, but he got cold feet before he made it to the front.

Ted Imperato, deputy chief of the national security division for the U.S. Attorney’s Office in Houston, said the court did not apply the sentencing guidelines properly and handed down an “unreasonably low sentence for such a crime,” when filing the initial notice that the government planned to appeal.

Khan’s trial lawyer, David Adler, said Friday he had not had time to review the appeal.

Seamus Hughes, deputy director of George Washington University’s Program on Extremism, which tracks cases around the country against homegrown terrorists, said Hughes’ sentence represents a significant departure from the norm. If Khan is removed from the equation, said the terrorism expert, the average prison sentence for that plea has been nearly 15 years.

“It is an abysmally low sentence for a material support to ISIS,” said Hughes, the GWU scholar. “The department of justice is laying down a marker because if the Khan sentence stands, it would have serious ramifications for the future sentencing of dozens of terrorism cases around the country. They want to make sure new sentencing bar isn’t set.”

At the sentencing, prosecutors recommended more than 20 years in prison and a lifetime of supervision for Khan.

Adler, Khan’s defense attorney, asked the judge for a downward departure from the guidelines, explaining that Khan had dedicated himself in recent years to work, school and family and had been speaking openly about his experience with young people who might consider joining terrorist groups.

“The man that stands here is a very, very, very different man than the stupid, naive man who believed this was a good thing to do,” Adler said at the hearing.

Khan, a U.S. citizen, was the second person in Houston to plead guilty to attempting to provide support for ISIS. Two others are awaiting trial: Warren Christopher Clark, a former substitute teacher from Sugar Land, who was captured this year in Syria, and Kaan Sercan Damlarkaya, an 18-year-old from Houston, who faces an addition charge of distributing information about building explosives.

Khan originally caught the attention of federal officials in McAllen while he was living in Australia in 2014. An agent testified that Khan sent a Facebook friend request to Sixto Ramiro Garcia, whom he knew from Klein Oak High School and a Houston-area mosque. Garcia had relocated to South Texas by the time the two made contact.

Khan admitted in his plea that he’d told Garcia, known as SRG, via Facebook that he wanted to join ISIS. A few weeks later, he told an alleged ISIS recruiter that he wanted to “die as a shahid,” or martyr.

Federal officials said Khan and Garcia made plans to meet in Turkey near the Syrian border. Garcia departed on Feb. 24, 2014, and Khan left for Istanbul the next day with plans to continue on to Syria, but he cut short the trip and returned to Houston after family members lied to him, saying his mother was in intensive care.

Garcia made it to Syria, where he sent panicked messages to his friend after Khan failed to show up.

Upon his return to Houston, Khan helped Garcia connect with an ISIS recruiter and sent him $200 or $300 to cover costs. By August 2014, Garcia made it to ISIS boot camp. On Dec. 25, 2014, Garcia's mother saw a notice on Facebook that her son had died fighting for the cause.

Khan, who is currently serving at a medium security facility in Arizona, is set to be released in early December.

Gabrielle Banks covers federal court for the Houston Chronicle. Follow her on Twitter and send her tips at gabrielle.banks@chron.com.